1. Field of the Invention
This invention relates to improvements in an actuator for a vibration prevention apparatus provided with a coil and a magnet.
2. Related Background Art
A system for preventing a hand fluctuation applied to a camera has heretofore been studied and there is one already carried on a product and put into practical use. Here, a system for preventing hand fluctuation will be briefly described.
Hand fluctuation of a camera during photographing usually is a vibration of a frequency of 1 Hz to 12 Hz, and as a basic idea for making a photograph free of image blur photographable even if such a hand fluctuation is caused at the point of release of a shutter release time, the vibration of the camera by the above-described hand fluctuation must be detected and in conformity with the detected value, a correction lens must be displaced. Accordingly, to make a free of image blur photographable even if hand fluctuation occurs, it is necessary to first detect the vibration of the camera accurately, and then to correct the variation in the optical axis due to the vibration of the camera.
Theoretically speaking, the detection of this vibration (camera vibration) can be accomplished by carrying on the camera a vibration detecting sensor for detecting acceleration, velocity or the like, and means for electrically or mechanically integrating the output signal of the vibration detecting sensor and outputting displacement. On the basis of this detected information, correcting optical means (comprising a correction lens and a fixed frame or the like for holding the correction lens) in a vibration prevention apparatus carried to make the photographing optical axis eccentric is controlled (the correction lens is displaced), whereby image blur correction becomes possible.
FIG. 10 of the accompanying drawings is an exploded perspective view of a vibration prevention apparatus used in the vibration prevention system of an interchangeable lens for a single-lens reflex camera. FIG. 11 of the accompanying drawings is a detailed view of the portion X (stepping motor unit) of FIG. 10. The epitome of the vibration prevention apparatus will hereinafter be described with reference to these figures.
This is a system in which a holder 101 holding a correction lens (not shown) is moved on a plane perpendicular to a photographing optical axis L by a driving force generated by coils 105p, 105y and magnets 107p, 107y to thereby correct camera vibration.
The reference 103 designates a restraining member in which two slots 103f and 103g formed about the photographing optical axis L are fitted on projections, not shown, projected from a ground plate 102, and the output of the stepping motor unit X which will be described later is transmitted to a gear portion 103a, whereby the restraining member 103 is rotated, and projected portions 101a to 101d (only two of which are seen in FIG. 10) provided at four locations on the holder 101 abut against the cam portions 103b to 103e, respectively, of the restraining member 103 so as to lock (restrain) the correction lens at a predetermined position. This is because when the vibration prevention apparatus is not being driven, the correction lens (and the holder 101) are swayed by the vibration or the like by the disturbance during the carrying of the camera, strike against the ground plate or the like, and make a crashing sound. In order to avoid being swayed, striking against the ground plate, making the crashing sound, and the damage thereby, it is necessary to provide a lock mechanism for holding the direction lens at a predetermined position during the non-operation of the apparatus.
The reference numeral 106 denotes a hard substrate (printed substrate) having mounted on its back photoreflectors 112p and 112y for the detection of positions corresponding to the movement positions of pitch and yaw on the holder 101 side, and having mounted thereon the terminal of the stepping motor unit X which will be described later, the terminals of coil units 105p and 105y and further, elements or the like concerned in the control of these. The reference characters 111p and 111y designate target members for position detection, and the target members 111p and 111y are printed with black and white patterns so that the outputs of the photoreflectors 112p and 112y may vary at a constant rate in conformity with the position of the correction lens.
The reference character X denotes a stepping motor unit of the conventional two-phase type, the reference characters 116a and 116b designate stator yokes obtained by piling up a plurality of metallic plates of a soft magnetic material and securing to one another, and the reference characters 115a and 115b denote coil for exciting the stator yokes 116a and 116b. The reference numeral 114 designates a rotor made of a plastic magnet rotatable by the excited state of the stator yokes 116a and 116b, and the outer periphery thereof is divisionally and alternately magnetized. The reference numeral 113 denotes a motor case lid which effects the positioning of the stator yokes 116a, 116b, the rotor 114 and the coils 115a, 115b, and is fixed to the ground plate 102 and forms the stepping motor unit X. A gear portion 114a provided on the rotor 114 meshes with the gear portion 103a of the restraining member 103 and the restraining member 103 is rotated to thereby lock the holder (correction lens) 110 as previously described.
In the aforedescribed vibration prevention apparatus according to the prior art, the position of the correction lens is always detected to perform an accurate correction driving and the output thereof is fed back. Also, as previously described, when the vibration prevention apparatus is not being driven, the correction lens or the like is swayed by the vibration or the like by the disturbance during the carrying or the like of the camera, strikes against the ground plate or the like, and makes a crashing sound. In order to avoid being swayed, striking against the ground plate, making a crashing sound, and the damage thereby, it has been necessary to provide a lock mechanism for locking the correction lens at a predetermined position. Therefor, a position detecting sensor for detecting the position of the correction lens and a part for locking the correction lens must be added, and this has led to disadvantages such as an increased cost and the enlargement of the size of the apparatus. Particularly, when an attempt is made to carry the vibration prevention apparatus on a compact camera or the like, the enlargement of the size of the apparatus as previously noted is fatal.
It is a first object of the present invention to provide a vibration prevention apparatus of which the enlargement of the size and complication of an apparatus can be prevented, the vibration can be suppressed with good accuracy, and the destruction by vibration or the like can be prevented.
It is a second object of the present invention to provide a vibration prevention apparatus in which the control of the gap between a coil and a magnet can be done easily.
The vibration prevention apparatus of the present invention has:
a holding member for holding an optical unit for correcting an image blur;
a support member for movably supporting the holding member;
a coil member provided on the holding member;
a magnet member provided on the support member, and disposed in opposed relationship with the coil member; and
a member disposed between the coil member and the magnet member, and having electrical conductivity;
wherein the coil member is electrically energized, whereby the holding member is driven relative to the support member.
Or conversely, the vibration prevention apparatus of the present invention has:
a holding member for holding an optical unit for correcting image blur;
a support member for movably supporting the holding member;
a magnet member provided on the holding member;
a coil member provided on the support member, and disposed in opposed relationship with the magnet member; and
a member disposed between the coil member and the magnet member, and having electrical conductivity;
wherein the coil member is electrically energized, whereby the holding member is driven relative to the support member.
When the holding member is driven by vibration an eddy current is generated in the electrically conductive member, and magnetic friction is caused. Thus, the electrically conductive member performs the role of a damper.
A further feature of the present invention is that the vibration prevention apparatus has an optical axis, and the holding member is biased relative to the support member by a plurality of biasing members. The optical unit is adapted to be maintained about the optical axis.
Also, the member having electrical conductivity is formed of a non-magnetic material.
Also, the member having electrical conductivity is a metallic plate.
Also, the member having electrical conductivity is fixed to the support member, or holding member.
Further features of the present invention will become apparent from the following description of some embodiments of the present invention.